Contoured implants, also called anatomical or teardrop-shaped implants, are shaped like a natural breast and create a sloped shape when placed over the chest muscles. Round breast implants have that, well, "round" Victoria's Secret or Playboy model shape. Contoured implants may flip over if the surgeon does not create the pocket correctly, resulting in a misshapen breast. Not true with round implants. If a round breast implant flips, it still looks the same. Your decision on implant shape should be based on how you want your new breasts to look.
Submuscular: the breast implant is emplaced beneath the pectoralis major muscle, without releasing the inferior origin of the muscle proper. Total muscular coverage of the implant can be achieved by releasing the lateral muscles of the chest wall—either the serratus muscle or the pectoralis minor muscle, or both—and suturing it, or them, to the pectoralis major muscle. In breast reconstruction surgery, the submuscular implantation approach effects maximal coverage of the breast implants. This technique is rarely used in cosmetic surgery due to high risk of animation deformities.